The present invention relates to a rhythm generating apparatus for an electronic musical instrument, which generates rhythm sounds like a percussion sound through digital signal processing.
In an electronic musical instrument, a rhythm generating apparatus is used to generate rhythm sounds like a percussion sound in an analog manner. However, the analog rhythm generating apparatus is complex and large in size. A compact electronic musical instrument which, is compact in size and light in weight thus can hardly be manufactured with such analog apparatus. Various attempts have been made to provide the rhythm generating apparatus in the form of a digital circuit. As an example, in Japanese Patent Disclosure No. 52-99,807/1977 published on Aug. 22, 1977, a rhythm generating apparatus generates digital waveform memory address signals corresponding to sounds of various kinds of instruments of percussion. An analog percussion signal is directly read out from a waveform memory. Therefore, the waveform memory has a relatively large capacity so that the sound generating circuit can hardly be arranged in an LSI. The rhythm generating apparatus thus remains large in size.
A rhythm generating apparatus for generating percussion sounds generally has a circuit for generating a noise type rhythm signal, which comprises a circuit for generating a noise signal and a circuit for producing a sound like a sound produced by cymbals by applying an envelope on the noise signal, and a circuit for generating a sine wave type rhythm signal to obtain a sound like a bass drum. The circuit for generating the noise type rhythm signal generally includes a multiplier which multiplies the noise signal by the envelope signal. As is well known, a digital multiplier is complicated and large in size, resulting in high cost.
Similarly, the circuit for generating the sine wave type rhythm signal includes a multiplier which multiplies the sine wave signal by the envelope signal. In general, an envelope signal generator and an envelope control circuit are arranged in the sine wave type rhythm signal generator and in the noise type rhythm signal generator, respectively. However, a piece of music rarely has a rhythm pattern simultaneously including the sine wave type percussion sound and the noise type percussion sound. In practice, the envelope signal generator and the envelope control circuit need not, therefore, be arranged in both rhythm signal generators.
Even if a plurality of rhythm sounds are involved with a musical performance, the same envelope waveform can be used and supplied to the rhythm signal generators without causing any trouble in the actual musical performance.
Further, in a conventional rhythm generating apparatus for generating more than two rhythm patterns, the volume of each rhythm sound is set to be constant, resulting in monotonous performance as compared with a musical performance by natural musical instruments. Thus, a rich musical expression can not be obtained.